1. Field of Invention
The present invention refers to an electric power supply for a switching regulator. The power supply falls within the class of switching power supplies and more specifically within the subgroup of power converters.
2. History of the Prior Art
The state of the art regarding power converters is presented in the paper: "Schaltnetzteile" (Switching Power Supplies) by Joachim Wustehube (Hrsg), Grafenau/Berlin, Federal Republic of Germany. Supplements to the state of the art are contained in the "Technical Newsletter 3/85," Siemens AG, Munich, Germany.
While existing switching controllers experience no problems under normal operating conditions, difficulties arise for existing switching controllers when they are subjected to extreme conditions and special requirements. Often these problems cannot be resolved at the same time or with the same process. Examples of such extreme conditions are:
short circuit
During fixed frequency operation, the direct short circuit of the secondary results in an almost complete breakdown of the output voltage V.sub.0 and a marked increase of the current. The short circuit is countered by shutting off the switching controller and then turning it on again with a soft starting circuit. PA1 Because a true no-load operation is not possible with the procedures and means known today, conventional solutions to the no-load condition include (1) skippig pulses of increasing size that produce a V.sub.0 &lt;=V.sub.Onominal when a maximum voltage V.sub.0 is reached in fixed frequency operation or (2) operating with the use of a built-in initial load. PA1 If two power converters with soft start circuits are connected in parallel, the probability that both will operate exactly in phase is infinitesimal. They will therefore impede each other during an attempt to re-power the system. PA1 Conventional operating procedures of switching controllers are based on a control oscillator that usually oscillates on a fixed frequency. A fixed frequency may be selected to avoid interference with an appliance powered by the regulator (for example, a TV set). In this case, only the keying ratio between turn-on time of the transformer primary winding and the period of the oscillation is variable. If the frequency is kept variable, however, it fluctuates between approximately 200 KHz and a few KHz depending on the operating conditions. The frequency reaches the audible range of the human ear at approximately 16 KHz. PA1 The disadvantages of conventionally known solutions are overcome. PA1 A procedure is established in which various operating circuits are covered. Among the latter, the following requirements are pointed out in particular:
If the short circuit persists, this procedure is repeated, which allows the current to increase repeatedly in accordance with the threshold characteristics.
no-load operation
sudden, severe load changes
large fluctuations of the input voltage
Examples of such special requirements are:
parallel operation of the switching controller
limited range of the switching frequency
Dimensioning of the input filters is therefore extremely difficult, and the switching controller becomes a source of acoustical interference.